U.S. patent number 6,553,284 [Application Number 09/826,537] was granted by the patent office on 2003-04-22 for process to prevent the overturning of a vehicle around its longitudinal axis.
This patent grant is currently assigned to WABCO GmbH & Co., OHG. Invention is credited to Hans Holst, Klaus Lindemann, Ingo Tha.
United States Patent |
6,553,284 |
Holst , et al. |
April 22, 2003 |
Process to prevent the overturning of a vehicle around its
longitudinal axis
Abstract
A process to prevent a vehicle, such as a tractor-trailer, from
overturning while negotiating a curve recognizes the potential for
overturning, and automatically activates a preventive braking
process. In addition, the automatic braking process is terminated
in a timely fashion to avoid overbraking the vehicle. This is
accomplished by subjecting at least one wheel on the inside of the
curve to a relatively weak braking force during the automatic
braking process, and by adjusting the braking parameters in
accordance with the vehicle's response characteristics.
Inventors: |
Holst; Hans (Velber,
DE), Lindemann; Klaus (Gehrden, DE), Tha;
Ingo (Hannover, DE) |
Assignee: |
WABCO GmbH & Co., OHG
(Hannover, DE)
|
Family
ID: |
7637750 |
Appl.
No.: |
09/826,537 |
Filed: |
April 4, 2001 |
Foreign Application Priority Data
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Apr 5, 2000 [DE] |
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100 17 045 |
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Current U.S.
Class: |
701/1 |
Current CPC
Class: |
B60T
8/17554 (20130101); B60T 8/243 (20130101); B60T
8/246 (20130101); B60T 8/248 (20130101); B60G
2300/042 (20130101); B60G 2800/0124 (20130101); B60G
2800/9124 (20130101); B60G 2800/922 (20130101); B60T
2230/03 (20130101) |
Current International
Class: |
B60T
8/1755 (20060101); B60T 8/24 (20060101); B60T
8/17 (20060101); G06F 017/00 () |
Field of
Search: |
;73/23.31,754,766,720,104,121,128,129,130 ;701/1,38,45,70-93 |
References Cited
[Referenced By]
U.S. Patent Documents
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6349247 |
February 2002 |
Schramm et al. |
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Foreign Patent Documents
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9602879 |
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Jul 1987 |
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DE |
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9802041 |
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Jul 1999 |
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DE |
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9907633 |
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Oct 1999 |
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DE |
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9936423 |
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Feb 2000 |
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DE |
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Primary Examiner: Williams; Hezron
Assistant Examiner: Harrison; Monica D.
Attorney, Agent or Firm: Proskauer Rose LLP
Claims
What is claimed is:
1. A process to prevent overturning of a vehicle around a
longitudinal axis of said vehicle when rounding a curve, in which
danger of overturning is evaluated, and braking is automatically
applied as required, comprising the following steps: a) applying a
first braking force to at least one first wheel of said vehicle,
wherein said at least one first wheel is on the inside of said
curve, b) wherein an indication of a potential overturning of said
vehicle requires a characteristic reduction of a rotational speed
of said at least one first wheel on the inside of said curve, c)
applying a second braking force to at least one second wheel of
said vehicle, wherein said at least one second wheel is on the
outside of said curve, to prevent said vehicle from overturning, d)
wherein said first braking force is weaker than said second braking
force, e) terminating said first and second braking forces when a
rotational speed of said at least one first wheel on the inside of
said curve accelerates in a predetermined characteristic
manner.
2. The process of claim 1, further comprising the following steps:
f) determining a transverse acceleration level of said vehicle, g)
comparing said transverse acceleration level to a predetermined
threshold level of said transverse acceleration, h) using the
difference between said transverse acceleration level and said
predetermined threshold level to indicate a potential overturning
of said vehicle.
3. The process of claim 1, wherein said indication of a potential
overturning of said vehicle further requires that a characteristic
reduction of said rotational speed of said at least one first wheel
on the inside of said curve is achieved.
4. The process of claim 3, wherein a verification is made to
ascertain whether a rotational speed of said at least one second
wheel on the outside of said curve remains essentially
unchanged.
5. The process of claim 4, wherein anti-lock braking system
slippage signals for said at least one first wheel on the inside of
said curve are disabled.
6. The process of claim 5, wherein a predetermined threshold level
of a transverse acceleration is varied as a function of the
vehicle's reaction to said first braking force.
7. The process of claim 5, wherein a predetermined threshold level
of a transverse acceleration is varied as a function of the
vehicle's transverse acceleration.
8. The process of claim 5, wherein said first braking force is
initiated only when a predetermined threshold level of a transverse
acceleration is exceeded.
9. The process of claim 8, wherein a plurality of transverse
acceleration signals derived from corresponding wheel rotational
speeds are used to improve the validity of a vehicle transverse
acceleration determination.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the control of a vehicle. More
specifically, the present invention relates to a process for
preventing a vehicle from overturning around its longitudinal
axis.
A process of this type is known from the German patent DE 196 02
879 C1, which is incorporated herein by reference.
This prior art process relates to recognizing the likelihood of a
vehicle overturning, and in particular, a vehicle consisting of a
tractor and a trailer. The danger of overturning is recognized
through a minimal actuation of the trailer brakes, combined with
the observation of the reaction of an ABS anti-lock braking system
incorporated in the trailer. If the ABS starts regulating and
carries out a locking prevention action in conjunction with this
relatively weak braking, there is an imminent danger of the
tractor-trailer overturning. Upon this situation occuring, either a
warning signal is emitted, or a stronger brake intervention is
carried out in order to reduce the transverse acceleration of the
tractor-trailer.
In addition to recognizing the right time to start such a
stabilizing braking intervention, it is also important to recognize
the right time to terminate the braking intervention. That is, at
the time when the danger of overturning is no longer acute, the
braking intervention should be reduced to avoid braking the vehicle
unnecessarily.
It is therefore an object of the present invention to disclose a
simple and reliable process for preventing a vehicle from
overturning around its longitudinal axis, in which a stabilizing
braking intervention is terminated in a timely manner.
SUMMARY OF THE INVENTION
A process to prevent the overturning of a vehicle around its
longitudinal axis, as e.g., when rounding a curve, automatically
evaluates the potential danger of overturning, and then proceeds to
apply braking as required, in the following manner: a) applying a
first braking force to at least one of the vehicle wheels on the
outside of the curve, to prevent the vehicle from overturning; b)
applying a second braking force to at least one of the vehicle
wheels on the inside of the curve, where the second braking force
is weaker than the first braking force; c) terminating the first
and second braking forces when a rotational speed of a wheel on the
inside of the curve accelerates in a predetermined characteristic
manner.
The inventive process determines the potential danger of
overturning by determining the transverse acceleration level of the
vehicle, based on the rotational speeds of the wheels, and
comparing this transverse acceleration level to a predetermined
threshold level. When the transverse acceleration level of the
vehicle exceeds the predetermined threshold level, a potential
danger of overturning is indicated.
The process further evaluates the danger of overturning by checking
a wheel on the inside of the curve to sense a characteristic
reduction of the wheel's rotational speed as a result of the second
braking force. At the same time, the process ascertains whether a
rotational speed of a wheel on the outside of the curve remains
essentially unchanged.
Where applicable, the process also disables the anti-lock braking
system slippage signals for a wheel on the inside of the curve when
the second braking force is applied.
One advantage of the present invention is that the time when there
is no longer a danger of overturning can be ascertained indirectly
from the wheel load; i.e., by evaluating the behavior of the wheel
with the lesser applied braking force. Using this technique, no
further information need be obtained, such as the level of the
center of gravity, or the actual transverse acceleration, which can
only be ascertained by a sensor. Therefore, no additional sensors
are needed, and the inventive process can be implemented very
economically through a simple expansion of the control program of
an electronic control device.
In the prior art processes to prevent overturning, in which the
wheels on both sides of the vehicle are subjected to approximately
the same, relatively high braking force, the wheels on the inside
of a curve don't show that slippage has decreased until the wheel
load is relatively great. This results in a calculated value of
transverse acceleration that is relatively high, which in turn
results in a continuation of the high braking force. Such a
relatively later termination of the ABS-regulation process is
regarded as uncomfortable. If the vehicle is braked in this manner
so that it almost comes to a stop, the further consequence may be
endangering the surrounding traffic. In the present invention,
however, a considerably lower braking force is applied to the
wheels on the inside of the curve, which results in an earlier
start-up of those wheels, and thereby to a lower calculated
transverse acceleration level, which enables the braking
intervention to be terminated earlier and more safely.
The present invention is applicable to conventional
compressed-air-controlled braking systems for utility vehicles, as
well as to braking systems using any other type of actuating
energy, such as hydraulic compression or electrical
servomotors.
Another advantage of the present invention is that the braking
intervention to prevent overturning is terminated when the
rotational speed of at least one wheel on the inside of the curve
accelerates in a characteristic manner. This eliminates the need
for a separate load sensor to recognize the load increase on the
wheel on the inside of the curve. Instead, the rotational-speed
sensor already included in an anti-locking system can also be used
for this purpose. It is a further advantage of the present
invention that the calculation for transverse acceleration requires
no special programming to recognize that there is no longer a
danger of overturning. Instead, the increasing rotational speed of
the wheel on the inside of the curve is included in this
calculation, which then shows a decrease of the transverse
acceleration level as shall be explained in further detail
below.
In the present invention, test braking with a relatively lower
braking force is applied to at least one wheel on the inside of the
curve, in order to recognize a potential danger of overturning.
Also, the ABS slippage signals of at least one wheel subjected to
the test braking are disabled. As a result, the wheel subjected to
test braking is not influenced by the ABS. It is therefore not
possible that the brake of the wheel subjected to the test braking
is bled by the ABS due to excessive wheel slip, and it is not able
to start up again. In contrast to a complete elimination of the ABS
function, this suppression of the ABS slippage signals enables the
anti-locking function to be maintained on the basis of acceleration
signals, for as long as the wheel has contact with the ground. This
helps to prevent damage to the tires, such as flat spots, for
example.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in greater detail below through the
example of an embodiment shown in the drawings, wherein
FIG. 1 shows a vehicle in a left curve, as seen from above;
FIGS. 2, 3 and 4 show a preferred embodiment of the invention in
flow-chart format, and
FIG. 5 shows the embodiment of FIGS. 2, 3, and 4 in the form of a
timing diagram.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1 shows a vehicle, consisting of a tractor vehicle 2 and a
semi-trailer 3, traveling in a left curve on a road 1 as seen from
above. While the present invention is applicable to this type of
tractor-trailer configuration, it is not limited to vehicles of
this type. The trailer 3 has a pneumatic braking system that
receives braking pressure from the tractor vehicle 2 in response to
a brake pedal actuation by the driver. The braking system can also
receive braking pressure by certain control and regulating
functions of the tractor vehicle 2. To supply these functions, the
tractor vehicle 2 is connected to the semi-trailer 3 via electrical
and pneumatic lines 11.
The tractor vehicle 2 and the semi-trailer 3 are rotatably
connected to each other at a pivot point 10.
The braking system of the semi-trailer 3 is preferably provided
with electrically actuated components, such as anti-lock braking
system (ABS) braking pressure modulators, or with purely
electrically powered brake actuators. The brake modulators, or
brake actuators, are controlled by an electronic control system 13.
The control system 13 and the brake modulators/brake actuators are
supplied with electrical energy and with the braking energy
pressure medium via electrical and pneumatic lines 12. In addition,
the rotational speed signals of the wheels 4, 5, 7, 8 (designated
as v.sub.4, v.sub.5, v.sub.7, v.sub.8) are inputted to the
electronic control system 13, as is known in the art of anti-lock
braking systems.
In the illustrated embodiment, the semi trailer wheels 4, 5, 6 are
on the outside of the curve, and the wheels 7, 8, 9 are on the
inside of the curve.
The electronic control system 13 executes a number of control and
regulating tasks in the semi-trailer 3. Importantly, one of these
tasks is to recognize a likely possibility of the vehicle 2, 3
overturning around its longitudinal axis, and to prevent such an
overturning action by means of a controlled braking intervention.
This preventive action is illustrated by an example flow chart in
FIG. 2.
The process starts at step 20. At step 21, the rotational speeds
v.sub.4, v.sub.5, v.sub.7, v.sub.8 of the wheels 4, 5, 7, 8 are
read in. In step 22, a first transverse acceleration signal
a.sub.q,1 is calculated from the rotational speeds v.sub.4,
v.sub.7, and a second transverse acceleration signal a.sub.q,2 is
calculated from the rotational speeds v.sub.5, v.sub.8 in
accordance with the following formulas:
The value S represents the wheel gauge of the vehicle. The
transverse acceleration signals a.sub.q,1, a.sub.q,2 are used
jointly in this illustrative embodiment in order to make the
process less prone to malfunctions, such as signal discrepancies,
different tire diameters, etc. In this manner, erroneous triggering
of the inventive process can be avoided.
In step 23, it is determined whether or not a braking force F.sub.2
had already been applied during a previous programmed execution of
the process to avoid overturning. If so, the inventive process
bypasses the sub-program block 26, to be described in detail in
conjunction with FIGS. 3 and 4, and branches off directly to step
24, where it is determined if there is still a danger of
overturning.
Referring again to step 23, if F.sub.2 has not already been
applied, the process continues with the sub-program block 26, which
is described in FIG. 3. This sub-program begins with a step 30. In
step 31, the process determines whether the first transverse
acceleration signal a.sub.q,1, and the second transverse
acceleration signal a.sub.q,2, exceed a predetermined transverse
acceleration threshold a.sub.q,krit. If so, the wheels 4, 5, 6, 7,
8, 9 of the semi-trailer 3 are subjected to a relatively low
braking force F.sub.1, as indicated in step 32. The braking force
F.sub.1 is set so that only a relatively slight braking effect
occurs, which is barely perceptible to the driver. Also, braking
force F.sub.1 is set so that no locking of wheels occurs, even on
road surfaces with a relatively low frictional value, if there is
no danger of overturning at this point. In a typical compressed-air
braking system, a braking force of approximately 1 to 2 bar is
applied in order to deliver the braking force F.sub.1.
Also in step 32, the ABS slippage signals for the wheels 7, 8 are
disabled, in order to avoid activation of the anti-locking function
due to high slippage. However, activation of the anti-locking
function based on acceleration signals continues to be enabled, so
that possible damage to the tires can be avoided.
In step 33, at the end of a sufficiently long build-up time for the
braking force F.sub.1, two evaluations are made. First, it is
ascertained whether the rotational speeds v.sub.7, v.sub.8 of the
wheels 7, 8 on the inside of the curve are characteristically lower
than the rotational speeds v.sub.4, v.sub.5 of the wheels 4, 5 on
the outside of the curve. This is done by comparing the sum of the
rotational speeds v.sub.7, v.sub.8 with the sum of the rotational
speeds v.sub.4, v.sub.5 times a factor K.sub.1. Then, the
rotational speeds v.sub.4, v.sub.5 are checked to see that they
remain essentially unchanged. This is accomplished by checking the
sum of the retardations of the wheels 4, 5; i.e., of the first time
derivation of the appertaining rotational speeds v.sub.4, v.sub.5.
Checking the wheels 4, 5 on the outside of the curve for continued
relatively high rotational speeds serves to avoid triggering the
inventive process by mistake, in the case of relatively low
frictional values; e.g., on an icy surface. In that type of
situation, it can happen that not only the rotational speeds of the
inner wheels (7, 8), are reduced intentionally by the banking force
F.sub.1 which is applied in the form of test braking, but also the
rotational speeds v.sub.4, v.sub.5 of the outer wheels are reduced
intentionally by the braking force F.sub.1, which is applied in the
form of test braking. In this case, the speed reduction of the
inner wheels 7, 8 does not presage an imminent overturning of the
vehicle 2, 3.
If both conditions of step 33 are met, it is assumed that there is
an imminent danger of overturning. At this point (step 34), the
wheels 4, 5, 6 on the outside of the curve, which have the better
frictional contact between road surface and tire, are subjected to
a braking force F.sub.2, that is greater than the braking force
F.sub.1. The level of braking force F.sub.2 is selected to
immediately reduce the vehicle speed, so that the transverse
acceleration, and thereby the danger of overturning, is also
reduced immediately. The physical relationship between the
vehicle's transverse acceleration a.sub.q and the vehicle speed v
is determined according to the following equation, where the value
R indicates the curve radius:
The anti-locking system prevents the wheels to which the braking
force F.sub.2 is applied from locking up. The weaker braking force
F.sub.1 continues to be applied to the wheels 7, 8, 9 on the inside
of the curve. In order to produce the braking force F.sub.2, a
pressure of 4 to 8 bar is preferably applied in a conventional
compressed air braking system.
In step 35, the transverse acceleration threshold a.sub.q,krit,
which is used to recognize a danger of overturning and to trigger
the test braking, is set to a starting value a.sub.q,start. This
will be described in further detail below, in an embodiment of the
invention wherein the transverse acceleration threshold
a.sub.q,krit can be varied.
The sub-program 26 then ends with a step 38.
Referring back to FIG. 2, if the decision in step 23 is yes, the
process continues at step 24. Here, a determination is made as to
whether or not the first transverse acceleration signal a.sub.q,1,
and the second transverse acceleration signal a.sub.q,2, fall below
the transverse acceleration threshold a.sub.q,krit. If they do fall
below, there is no longer any danger of overturning, and the
braking forces F.sub.1, F.sub.2 can be terminated in step 25. In
addition, the ABS slipping signals, which were disabled in step 32
of FIG. 3, can be released. If the first and second transverse
acceleration signals a.sub.q,1 and a.sub.q,2 do not fall below the
transverse acceleration threshold a.sub.q,krit (step 24, FIG. 2),
the process bypasses block 25, and branches directly to step 27,
where the process ends.
The above described inventive process, and especially the
utilization of the transverse acceleration signals a.sub.q,1,
a.sub.q,2, can be summarized as follows. When a danger of
overturning threatens, the wheels 7, 8, 9, having a lighter load on
the inside of the curve, tend towards a decreased rotational speed
due to the test braking force F.sub.1. This causes a relatively
large difference in rotational speed between the wheels on the
inside and those on the outside of the curve. By applying the
equations [1] and [2], this difference results in a rapid increase
of the first and second transverse acceleration signals a.sub.q,1,
a.sub.q,2. On the other hand, the return of the wheels 7, 8, 9 to
the road surface; e.g., as a result of the larger braking force
F.sub.2 in step 34 of FIG. 3, causes the calculated transverse
acceleration signals a.sub.q,1, a.sub.q,2 to decrease rapidly. Due
to this rapid change in the transverse acceleration signal levels,
the test braking force F.sub.1, which stops the wheels bearing the
lesser load when there is a danger of overturning, can be used to
recognize the return of the wheels to the road surface, indicating
the end of the danger of overturning. Under these conditions, the
wheels on the inside of the curve start up again due to the
increasing wheel load, in spite of the effect of braking force
F.sub.1, resulting in a characteristic increase in rotational
speeds v.sub.7, v.sub.8.
Referring again to FIG. 3, if one or both conditions checked in
step 33 are not met, the transverse acceleration threshold
a.sub.q,krit is increased by a value K.sub.3 (step 36), and the
process branches off to step 38, where it ends. Steps 36, 35, and
sub-program step 37 are part of an embodiment of the invention to
be explained in further detail below.
If one or both conditions checked in step 31 are not met, the
process branches off to the sub-program block 37, which is shown in
further detail in FIG. 4.
The sub-program 37 starts at step 40. In step 41, the test braking
force F.sub.1 is terminated. Also, the ABS slippage signals that
had been disabled in step 32 are released. The process then
continues with step 42, where the condition previously checked in
step 24 (FIG. 2) is evaluated. This evaluation determines whether
the termination of the brake intervention has fallen short by a
given value K.sub.4. That is, it is ascertained whether every
transverse acceleration signal a.sub.q,1, a.sub.q,2 falls short of
the transverse acceleration threshold a.sub.q,krit by a value
K.sub.4. If this is true, then the vehicle 2, 3 is relatively safe
from the danger of overturning, and the transverse acceleration
threshold a.sub.q,krit, which was raised by a value K3 in step 36
(FIG. 3), can be lowered with little risk of erroneously triggering
the process to prevent overturning. However, the lowered level of
the transverse acceleration threshold a.sub.q,krit must not fall
below a certain minimum value K.sub.5, which is predetermined as a
function of the vehicle characteristics.
This condition is checked in step 43. If it has been met, the
transverse acceleration threshold a.sub.q,krit is decreased in step
44 by a value K.sub.6, and the process ends at step 45. However, in
the event of a negative result of the check in step 42 or 43, the
process moves directly to step 45.
A starting value a.sub.q,start of the transverse acceleration
threshold a.sub.q,krit can be predetermined and stored as a
parameter in a non-volatile memory, based on the characteristics of
the vehicle. In an advantageous embodiment of the present
invention, this starting value may be determined in dependance of
the vehicle loading; e.g., by measuring the pressure in the air
suspension bellows when the vehicle is so equipped.
Two typical applications of the inventive process are illustrated
in the timing diagrams of FIG. 5. One application depicts a vehicle
traveling on a curve with no danger of overturning, and the other
application depicts a vehicle traveling on a curve with imminent
danger of overturning. The above described signal magnitudes are
represented as velocity values in FIG. 5a, as transverse
acceleration values in FIG. 5b, and as braking forces F (or braking
pressures p) for both left and right sides of the vehicle in FIG.
5c. All the figures (5a, 5b, and 5c) have a common x-axis time
base. In order to simplify the representation, only the rotational
speed signals v.sub.4, v.sub.7 (of the wheels 4, 7) of the semi
trailer 3 are considered, in addition to the signals a.sub.q,1,
a.sub.q,krit derived from them. The inventive process can also
apply to vehicles with only one axle, or with only one axle
equipped with rotational speed sensors.
Starting at time t.sub.0, the vehicle 2, 3 travels in a straight
line at a normal speed. At this time, the rotational speeds
v.sub.4, v.sub.7 have identical values, and the transverse
acceleration signal a.sub.q.1 has a value=0. At time t.sub.1, the
vehicle 2, 3 begins to travel into a left curve as shown in FIG. 1.
At the same time, the rotational speed v.sub.7 (on the inside of
the curve) decreases relative to the rotational speed v.sub.4 (on
the outside of the curve), where a relatively small decrease in
rotational speed v.sub.4 is caused by the semi-trailer 3. This
small decrease in rotational speed v.sub.4 is considered
negligible, however, and is disregarded in FIG. 5a.
Due to the difference between the rotational speeds v.sub.4 and
v.sub.7, the transverse acceleration signal a.sub.q,1 increases
(Equation 1), and at time t.sub.2, reaches the transverse
acceleration threshold a.sub.q,krit. As a result, the test braking
action is triggered at all the wheels (4, 5, 6, 7, 8, 9) of the
semi-trailer 3 in FIG. 1. This is illustrated in FIG. 5c by an
increase in braking force to the value F.sub.1 (signals 50, 51).
Furthermore, the transverse acceleration threshold a.sub.q,krit is
increased, in accordance with every embodiment of the inventive
process depicted in FIGS. 2 to 4. Illustratively, this increase can
be made in fine-tuned steps (K.sub.3 in step 36 of FIG. 3) over
intervals of 10 ms, as indicated by the ramp-shaped rise in FIG.
5b. At time t.sub.3, the transverse acceleration signal a.sub.q,1
falls below the transverse acceleration threshold a.sub.q,krit, and
this results in a termination of the test braking action (FIG. 5c).
The transverse acceleration threshold a.sub.q,krit, which had been
increased between times t.sub.2 and t.sub.3, is initially
maintained, since no serious danger of overturning was recognized
in this time period. As such, the higher transverse acceleration
threshold a.sub.q,krit is compatible with safety, since it can be
assumed that the critical value of transverse acceleration is
higher when there is a danger of overturning than the transverse
acceleration threshold a.sub.q,start, which was assumed at the
start of vehicle travel.
At time t.sub.4, the condition in step 42 (FIG. 4) is met; i.e.,
the transverse acceleration signal a.sub.q,1 (FIG. 5b) falls below
the transverse acceleration threshold a.sub.q,krit by a value
K.sub.4. Therefore, the transverse acceleration threshold
a.sub.q,krit is decremented in fine-tuned steps (K.sub.6 in step
44, FIG. 4) for as long as the transverse acceleration threshold
a.sub.q,krit is larger than the minimum value K.sub.5 (step 43 in
FIG. 4). This is illustrated in FIG. 5b by the ramp-shaped waveform
between times t.sub.4 and t.sub.5. At time t.sub.5, the transverse
acceleration threshold a.sub.q,krit has reached the minimum value
K.sub.5, so that the condition verified in step 43 is no longer
met, and the transverse acceleration threshold a.sub.q,krit remains
at the minimum value K.sub.5. In this manner, the transverse
acceleration threshold a.sub.q,krit is adjusted as a self-learning
function, in order to match the actual conditions of travel, in
accordance with the embodiments of the process shown in steps 35,
36, and 42, 43, 44 of FIGS. 3 and 4, respectively.
Referring again to FIG. 5, the vehicle 2, 3 has ended its curve
travel (time t.sub.5), which leads to an adjustment of the
rotational speeds v.sub.4, v.sub.7 to match each other, and to a
return of the transverse acceleration signal a.sub.q,1 to a
value=0. At time t.sub.6, the vehicle 2, 3 again travels into a
left curve, but this time with a danger of overturning, so that the
inventive process of recognizing and preventing such a mishap can
be explained. Starting at time t.sub.6, the rotational speed
v.sub.7 (on the inside of the curve) decreases, while the
rotational speed v.sub.4 (on the outside of the curve) remains
essentially constant for the reasons previously discussed. At time
t.sub.7, the transverse acceleration signal a.sub.q,1 exceeds the
transverse acceleration threshold a.sub.q,krit, causing the test
braking action to be initiated (signals 52, 53 in FIG. 5c), and the
transverse acceleration threshold a.sub.q,krit is again increased
in a ramp-like manner. At approximately time t.sub.8, the load on
wheel 7 is reduced to such an extent that the test braking force
F.sub.1 on the wheel 7 rapidly reduces the rotational speed
v.sub.7, as can be seen in FIG. 5a. This rapid reduction of the
rotational speed v.sub.7 causes a brief decrease (54) of the
braking force on the wheel 7 shortly after time t.sub.9, due to the
action of the anti-locking function.
At time t.sub.9, the criteria listed in step 33 (FIG. 3) are met,
with constant K.sub.1 assumed to have an illustrative value of 0.5
(see dashed line 56 in FIG. 5a). Therefore, an imminent danger of
overturning is present. Starting at time t.sub.9, a braking force
F.sub.2 (signal 55 in FIG. 5c) is applied to the wheel 4 (on the
outside of the curve), as well as to the other wheels 5, 6 on the
outside of the curve. Due to this braking force F.sub.2, the
vehicle 2, 3 decelerates, as can be seen in FIG. 5a from the
downward sloping of the rotational speed v.sub.4.
Also at time t.sub.9, the transverse acceleration threshold
a.sub.q,krit is set back to the starting value a.sub.q,start (step
35 in FIG. 3).
Due to the rapid reduction of the rotational speed v.sub.7, the
transverse acceleration signal a.sub.q,1 increases to a maximum
value when the rotational speed v.sub.7 is reduced to 0. Due to the
reduction of the vehicle's traveling speed, and the accompanying
reduction of the rotational speed v.sub.4, the transverse
acceleration signal a.sub.q,1 also decreases.
At time t.sub.10, the wheel 7 resumes its rotational movement, thus
increasing the rotational speed v.sub.7. At time t.sub.11, the
transverse acceleration signal a.sub.q,1 falls below the transverse
acceleration threshold a.sub.q,krit, which had been set back to the
level a.sub.q,start at time t.sub.9. This results in the immediate
termination of the braking intervention. Finally, at time t.sub.12,
the vehicle 2, 3 is again represented as traveling on a straight
course.
Illustratively, the following values are preferred for the
magnitudes K.sub.1, K.sub.2, K.sub.3, K.sub.4, K.sub.5, K.sub.6,
a.sub.q,start: K.sub.1 =0.5 K.sub.2 =5 m/s.sup.2 K.sub.3 =0.01
m/s.sup.2 K.sub.4 =1 m/s.sup.2 K.sub.5 =5 m/s.sup.2 K.sub.6 =0.01
m/s.sup.2 per second a.sub.q,start =3 m/s.sup.2
While the invention has been described by reference to specific
embodiments, this was for purposes of illustration only and should
not be construed to limit the scope of the invention. Numerous
alternative embodiments will be apparent to those skilled in the
art.
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